(a) Field of the Invention
The present invention relates to a shift register and a gate driving circuit of a display device using the same, and more particularly, to a shift register, which can adjust a scan direction when a screen of a display device is upside down, and a gate driving circuit of the display device using the same.
(b) Description of the Related Art
Occasionally, a display device that has recently been used in a portable terminal may display images on a screen as it is reversed up and down or left and right in accordance with a user's intention. For these cases, a gate driving circuits of the display device need to be designed to change a scan direction.
A conventional shift register includes a plurality of thin film transistors (TFT) as disclosed in Korean Patent No. 10-1020627.
FIG. 1 is a block diagram of a gate driving circuit, showing connection among the conventional shift registers capable of adjusting the scan direction. FIG. 2 is a view of illustrating an example of the conventional shift register shown as a block in FIG. 1.
Referring to FIG. 2, the conventional shift register includes an input unit 10 for receiving an input signal for a shifting operation, an inverter unit 20 and a reset unit 30 for improving at its off-characteristics in an output terminal, and an output unit 40 for outputting a scan signal to a corresponding gate line.
In the conventional shift register, the inverter unit 20 is basically consisted of a TFT T5 and a TFT T9. The TFT T5 constantly keeps turned on by a bias voltage Vbias, and the TFT T9 is biased by voltage difference between VGL and LVGL since voltage applied to a source of the TFT T9 is a voltage of LVGL. Thus, even if the TFT T9 is turned on, an X node cannot be entirely dropped into the voltage of LVGL. Further, even when the TFT T9 is turned off, the X node cannot be increased up to the bias voltage Vbias. Therefore, the X node cannot be fully inverted.
To compensate for insufficient driving performance for the TFTs and secure reliability, a conventional inverter further need to include two TFTs T6 and T8 in addition to the TFTs T5 and T9. Thus, the conventional inverter includes all four of TFTs, and adds an LVGL signal to improve the reliability. Like this, such a conventional shift register needs a plurality of thin film transistors and signal lines to improve the off-characteristics. This causes problems of enlarging a dead space of a display device, resulting in the display having bigger size than originally planned and modifying a structure of the gate driving circuit.
Further, a shift register of a recent gate driving circuit has an additional function to change the order of applying signals to gate lines depending on rotation of a display screen. To this end, as shown in FIGS. 1 and 2, the conventional shift register needs a scan direction adjuster 50 including four thin film transistors Tb, Tbr, Tf and Tfr. Like this, as the number of transistors increases in order to change the order of applying the signals to the gate lines, the foregoing problems become serious to the conventional shift register.